Non-contact acoustic filtering of particles by a standing wave field

Non-contact micromanipulation is one of the fundamental techniques in micromachine technology. In the previous paper at MHS2000, a new manipulation technique was proposed to transport a particle three-dimensionally using an ultrasonic standing wave field generated by four transducers, whose sound beam axes were arranged to cross at a point with the same angle. There is a request from industry to operate a lot of flowing particles continuously. The present paper describes non-contact concentration of suspended particles in flow using acoustic radiation pressure in water. Using a standing wave field generated between a transducer and a reflector, it is possible to trap particles at nodes of the sound pressure distribution and to move their positions by changing the frequency. Thus, a standing wave field was generated in a wide area by a rectangle transducer along the flow route, and filtering of particles was tried. As a result, it was possible to draw particles to the reflector side or the transducer side by changing the frequency in repeat sweep mode. Namely, this method makes it possible to concentrate particles continuously.